A number of processes for preparing certain compounds of formulae 1 and/or 2 have been described in the literature. For example, Morin et al., J. Am. Chem. Soc. 91, 1401 (1969), have shown that treatment of phenoxymethyl penicillin sulfoxide methyl ester with acetic anhydride gave a mixture of the corresponding 2-acetoxymethyl penicillin ester with the corresponding 3-acetoxy-3-methylcepham derivative from which both compounds could be isolated in poor yields by chromatography. Gutowski, U.S. Pat. No. 3,668,201 issued June 6, 1972, has converted certain penicillin sulfoxides by treatment with acids, preferably sulfuric or sulfamic acid or salts thereof, into the corresponding 3-hydroxy-3-methylcepham derivatives, and Foster et al., U.S. Pat. No. 3,668,202 issued June 6, 1972, improved that process by using a tertiary carboxamide containing solvent. Kukolja et al., J. Am. Chem. Soc. 97, 3192 (1975), have shown that 2.alpha.-chloromethylpenam derivatives give the corresponding 2.alpha.-acetoxymethylpenam derivatives when treated with silver acetate in acetic acid, and that the corresponding 2.beta.-chloromethylpenam derivatives give a mixture of the corresponding 2.beta.-acetoxymethylpenam derivative with the corresponding 3.beta.-acetoxy-3.alpha.-methylcepham derivative and the corresponding 3-methylcephem derivative. Kamiya et al., U.S. Pat. No. 3,954,732, issued May 4, 1976, have described, inter alia, the transformation of unsym-azetidinone disulfide derivatives by treatment with various nucleophiles into 2-(substituted methyl)penam and/or 3-substituted-3-(lower alkyl)cepham derivatives. Fujisawa Japanese Patent Publication 9082-691, published August 8, 1974, discloses the reaction of an unsym-azetidinone disulfide with silver acetate in t-butanol to give the corresponding 2-acetoxymethylpenam derivative.